Textile fabrics are widely employed as reinforcement in various industrial products, such as hoses, conveyor belts, tires, power transmission belts and the like. In the production of such products, it is a practice to combine the reinforcement fabric with the uncured rubber carcass, substrate, or core of the final product during a vulcanizing operation such that heat curing bonds and adhesively secures the reinforcement fabric in intimate association with the rubber base of the product. To improve the cured adhesion and bonding of the reinforcement fabric to the rubber substrate, it is a practice to precoat the fabric with an adhesion-promoting composition, such as an uncured neoprene solvent or latex system.
In precoated reinforcement fabrics employed in power transmission belts, the coated reinforcement fabric may be employed as an intermediate reinforcement layer in the rubber core, as well as cut into a narrow strip which is folded about the longitudinal axis of the uncured rubber belt core, with side edges and end portions of the fabric strip disposed in overlapping relationship to form an outer protective covering for the core. In such cases, difficulties have been encountered in maintaining positive mechanical positional securement of the fabric to the rubber core, and especially the overlapped portions of the cover fabric to each other in preparing the belt for vulcanization cure in a mold. If intimate mechanical securement of the reinforcement fabric to the rubber carcass and to itself at the positions of fabric overlap is not obtained and maintained, the effective life of the belt can be greatly reduced by early separation of the fabric from the rubber core due to poor vulcanization bonding thereto.
It is therefore desirable to provide in these and like instances of uses of reinforcement fabrics a coated fabric which, at the time of vulcanization, has a highly tacky, or sticky, uncured rubber-coated surface to maintain intimate, positive mechanical adhesion of the fabric to the rubber core and to the overlapped fabric portions of the belt in preparation for and during the curing operation. Such uncured, surface stickiness in the coated reinforcement fabric is referred to herein as "open green tack". If such reinforcement fabrics are manufactured and precoated by a fabric manufacturer for later shipment, in roll goods form, to a belt manufacturer for incorporation into the final product, the coated reinforcement fabric may be coated weeks or even months before it is finally combined with the uncured rubber substrate in a final curing operation. Thus, it is essential that the coated fabric possess a long "open green tack" shelf life, in order that the reinforcement fabric does not lose its surface stickiness before it can be incorporated into the final product.
In rubber-based adhesive systems, it has heretofore been proposed to employ various organic components to impart tackiness or stickiness to the adhesive. Such components are generally referred to in the art as tackifiers. Although tackifiers perform the function of softening and improving the stickiness of a neoprene composition coating, they relatively quickly lose their uncured stickiness, or tack, after being coated on the fabric. Also, tackifiers inherently, because of their plasticizing nature, tend to reduce the amount of adhesion which can be obtained between the coated reinforcement fabric and the rubber substrate in final cured state. Thus, it has been difficult for a textile manufacturer to produce a precoated reinforcement fabric which has sufficient long open green tack shelf life to provide a belt manufacturer with time flexibility in use of the fabric in belt manufacture with the necessary cured adhesion in the final vulcanized product.
In addition to the above mentioned difficulties in developing uncured adhesion coatings and compositions exhibiting long open green tack shelf life without detrimentally affecting necessary adhesion values in cured state, many of the known tackifiers are incompatible for incorporation into various neoprene systems. Often the tackifiers cannot be uniformly dispersed in the adhesive composition, or, if dispersible therein, do not remain uniformly dispersed therein for any extended period of time. Thus, when such compositions are to be used for coating reinforcement fabrics on a large scale commercial, continuous coating operation where the coating composition must be available in large amounts and in uniformly dispersed condition for extended periods of time, many if not most of the possible compositions are unacceptable.